Metal-free solvent promoted oxidation of benzylic secondary amines to nitrones with H202

An environmentally benign protocol for the generation of nitrones from benzylic secondary amines via catalyst-free oxidation of secondary amines using H2O2 in MeOH or CH3CN is described. This methodology provides a selective access to a variety of C-aryl nitrones in yields of 60 to 93%. Several studies have been performed to shed light on the reaction mechanism and the role of the solventWe thank FEDER/Ministerio de Ciencia, Innovación y Universidades−Agencia Estatal de Investigación (Grant PGC2018-098660-B-I00) and CAPES (Finance Code 001), CNPq (310514/2018-5), FAPEMIG for financial suppor

Síntese de catalisadores de nióbio suportados em óxidos mistos e suas aplicações em reações com aminas primárias

A series of mixed metal oxides-supported niobium-based heterogeneous catalysts, prepared and characterized, was tested towards reactions with benzylamine and substituted benzylamines. The harmless and inexpensive hydrogen peroxide was employed as oxidizing agent aiming the formation of benzaldehyde oxime as main reaction product. The reactions were carried out under visible low spectrum violet light and led to good conversion rates from starting material but only modest selectivity was achieved based on gas chromatography–mass spectrometry data. When the reactions were performed at 50 °C in the presence of the niobium-based catalyst, it was possible to raise the selectivity for oxime as main product up to 70 %. The substrate scope using different substituted benzylamines was well tolerated and led to good isolated yields, suggesting the use of supported niobium-based catalysts, under mild oxidative conditions, as a reasonable method for the direct conversion of primary amines into their corresponding oximes.Uma série de catalisadores heterogêneos, constituídos por nióbio suportado em óxidos metálicos mistos de Al, Zn e Mg, devidamente preparada e caracterizada, foi testada frente a reações com benzilamina e benzilaminas substituídas. O peróxido de hidrogênio, um agente oxidante inofensivo e de reduzido custo, foi empregado visando a obtenção de benzaldeído oximas como produtos de reação. As reações, inicialmente conduzidas em presença de luz violeta, levaram a boas conversões do material de partida, entretanto, apenas uma modesta seletividade para a correspondente oxima foi alcançada, de acordo com as análises por cromatografia gasosa acoplada a detector de massas. Quando estas reações foram realizadas em 50 °C, na presença dos catalisadores de nióbio, foi possível obter excelentes conversões da amina de partida, apresentando seletividade acima de 70 % para oxima como produto de reação. Um escopo de substratos utilizando diferentes benzilaminas substituídas revelou-se bem tolerado, levando a bons rendimentos isolados, sugerindo o uso de catalisadores baseados em nióbio, em condições brandas, como um método razoável para a conversão direta de aminas em oximas.CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológic

Screening method for determination of C18:1 trans fatty acids positional isomers in chocolate by 1H NMR and chemometrics

The regulations established worldwide, restricting trans fatty acids (TFA) from industrial origin in foods, encourage the development of rapid methods to verify the quality of food products. A simple and rapid procedure based on 1H NMR combined with multivariate calibration was developed to quantify C18:1 TFA isomers in chocolate fat. Thirty chocolate samples (milk, dark and white chocolates) were analyzed by 1H NMR, and also by a reference gas chromatographic method. Then, partial least squares regression was used for model development. The most important 1H NMR signals for the modeling comprised the 5.25–5.45 ppm region, corresponding to CH (double bonds and glycerol backbone), and the 1.94–1.99 ppm region, characteristic of CH2 allylic to trans double bonds. Good predictive qualities for all TFA isomers were obtained. Coefficient of correlation for prediction was 0.967 for C18:1 trans 6–8; 0.981 for C18:1 trans 9; 0.987 for C18:1 trans 10; 0.941 for C18:1 trans 11; 0.983 for C18:1 trans 12 and 0.977 for total TFA. This study demonstrates the potential of 1H NMR to be applied in food industries in order to perform TFA control analysis as well as to investigate food fraud.This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 and PDSE 88881187078/2018–01; Spanish Ministry of Economy and Competitiveness (AGL2016-75159-C2-2-R); CNPq (303355/2017–4, 424032/2018–0); Finep (CT-INFRA 01/2013-REF 0633/13); RQ-MG (CEX.RED- 00010–14), and INCTBio (FAPESP 2014/50867–3, CNPq 465389/2014–7).Peer reviewe

Lipid classification of fish oil omega-3 supplements by 1H NMR and multivariate analysis

The worldwide advent of concentrated supplements containing omega-3 fatty acids (FA) in the form of triacylglycerols (TAG) or ethyl esters (EE) has increased the interest in developing methods to classify these products. The quality control based on their lipid composition has become necessary since EE bioavailability has been proved to be lower when compared to the TAG. In this preliminary study, eight models based on 1H NMR and supervised discriminant analysis (PLS-DA/OPLS-DA) were applied to classify omega-3 fish oil in TAG or EE forms. The 4.0–4.5 ppm region was selected for modeling since it bracketed spectral features to discriminate TAG and EE. The non-supervised principal component analysis was employed to visually evaluate the distribution of samples and revealed a clear separation of TAG from EE marine oils along PC1. In addition, representative TAG and EE samples were 100 % correctly classified using any of the eight supervised models studied. The developed models resulted in high R2Y (≥ 0.977) and Q2 (≥ 0.953), and low root mean square error for prediction (≤ 0.009), which demonstrates the high potential of this rapid and straightforward procedure to evaluate the lipid form of supplements and mislabeling.We would like to acknowledge the Spanish Ministry of Economy and Competitiveness (AGL2016-75159-C2-2-R); CAPES (PDSE 88881187078/2018-01, PNPD 23071022702/2018-43); CNPq (303355/2017-4, 424032/2018-0) and INCTBio (Projects FAPESP 2014/50867-3 and CNPq 465389/2014-7) for the fellowships and financial support.Peer reviewe